Brushholder



Aug. 25, 1931.

INVENTOR #Lb/'ry FIL/@ffm am.

A TORNEY Patented Aug. 25, 1931 UNITED STATES PATENT OFFICE HARRY F. IHIARTIMIAN,` OF PITTSBURGH, PENNSYLVANIA,` ASSIGNOR T WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA BRUSHHOLDER Application led October 11, 1929. Serial No. 338,891.

My inventionrelates to brushholdersfor dynamo-electric machines, and it has more particular 4relation to brushholder fingers and the supporting shafts therethrough, especially in connection with alternatingcurrent railway motors, although it is susceptible, of course, of other juses.

Carbon brushes are preeminently the best for use in the current-collecting devices of dynamo-electric machines and are almost universally used. These brushes must, lin

general, be pressed down against the commutator cylinder or collector ring by means of a spring-pressed brushholder finger which bears against vthe top of the brush. The top of the brush may, or may not, be covered with metal. i

Heretofore, it has been customary to make the brushholder-finger tips of hard-drawn copper, which was the best known-contact material, priorfto my present invention, for withstanding the chattering on the top of theA carbon brush.

It has long been known that small quantities of'tin or other metals, when alloyed with copper, increase the f strength of the metal but also very rapidly decrease the conductivity as the quantity of the alloying metal is increased. It has also been known that, when cadmium is utilized as the alloying metal, it gives practically the .same increase .instrength without nearly as great a decrease in the conductivity. It has not been known, however, that a cadmium-copper alloy is far less affected by arcing;'that is,

'that it will not be eaten away and chipped off' when subjected to the tiny arcs and chattering whieh are likely to occur at the point of contact between the brushholder finger and the brush. A 4long investigation of means for increasing the life of' brushholdery fingers or of the finger tips therefor has not revealed any better commercially obtainable material than cadmium-copper alloy, which is capable of withstanding the arcing and pounding to which these lingers are subjected. The alloying of between one-half and one percent of cadmium with substantially pure copper about triples the life of the finger tip, as compared with what it was with hard-drawn copper.

With a brushholder finger tip having such increased life, it becomes practicable to join the finger tips non-removably to the rest of the brushholder, finger, and. I have found that the cost of the brushholder finger may be reduced more than fifty per cent by casting the same from a lightaluminum alloy having a lower melting poin't than the cadmium-copper nger tip, and causing the stem of the finger tip to so project into the mold as to be surrounded by the aluminum alloy and thus be anchored into place as an integral part of the lbrushholder finger.

While aluminum alloys, in general, have the property of fiowing readily in molding, the alloys of the silicon group are as easy fiowing as any, and the particular alloy having about 12% or 13% of silicon, with the rest ,substantially` pure aluminum, (although about one-half of one percent of -iron may easily be tolerated), is the strongas the best'material for my cast brushholder,

finger and upon this particular 12% or 13% silicon-aluminum alloy` which is preferred.

As a further development of my brushholder finger, particularly designed ,for alj ternating-current commutator motors for railway service, although it is obviously not` limited thereto, I have sought to double the life of the brushholder fingers heretofore.

used, and this has necessitated a change` in the shaft which supports the brushholderV finger. During my investigation, I have developed a special testing machine 'ving an indication, in 100 hours,y ofthe urabihty of, for instance, an aluminum-tobronze bearing having two years life in service.

ing, so far, as its bearing qualities are con-.

cerned.

The graphitized micarta, which I now utilize for all brushholder shafts, is a .graphitized molded-composition product having a cloth base, as will be subsequently described. It gives a longer life of shaft than any metal shaft material that I have ever experimented with for this type of service; it gives and maintains a free movement of shaft, thereby increasing the life ofthe finger tip (and increasing the life of the cast aluminum-atloy portion of the brushholder finger, whereasfthe bronze shaft for the aluminum finger would get tight, due to dragging of the aluminum, Vafter a certain time; it has a high electrical resistance and 4j 40.,-

is of such naturethat any current that Amay be transmitted from the moving finger will not cause it to pit, thereby eliminating any chancefor the finger to freeze or stick to it; and it does not absorb moisture and does not requirea finish or plating on the shaft tg keep it from rusting, and, therefore, my new graphitized micarta shafts may be readily stocked over a long period of time.

All of the above-mentioned developments have been worked' out at very considerable cost, by more or less empirlcal methods, and

' lI. desire to secure patent protection covering .these contributions to the art.

l In the accompanyingdrawings,

Figure 1 is a longitudinal sectional view through a complete brushholder embodying myinvention, in a form desirablefor use.

in alternating-current railway motors, showing the carbon brush 1n place, and an outline of the commutator cylinder or'shp ring Aupon which the brush bears, and

Fig. 2 is a sectional View through the hub of the brushholder finger, on a plane indicated by the line II-II in Fig. l.

The brushholder nger ,illustrated in the drawings is of the same general type as that shown in lal patent of J. V. Dobson No.

1,533,237, granted April 14:, 1925, and assigned to the Westinghouse Electric and Manufacturing Company, and my o wn Putent No. 1,569,367, granted January l2, 1926.

The brushholder 1 supports a carbon brush 2 which bears on a commutator `cylinder or other current-collecting cylinder 3.

The brushholder carries a shaft 4 which supports'a brushholder finger 5 having an enlarged hub 6 which is mounted for movement around said shaft.

The hub'is provided with an annular recess 7 which is open at one end and is adapted to house a helical spring 8. The brushholder finger 5 is provided with a separate finger tip 9 which bears against the top of the brush 2.

As hereinabove described, my finger tip 9 Ais made of cadmium-copper" and is provided with a stem l0 which is embedded in the material of the rest of the brushholder finger-which is cast around it. This brush.- .z

holder finger material is preferably a silicon alloy ofaluminum, as already described.

As also mentioned hereinabove, the shaft A4 is made of raphitized micarta. This material is pre erably prepared by mixing 1 0 gallons of bakelite-varnish with 22.5 pounds of graphite. The micarta is then thinned with a solvent, such as a mixture of alcol.

hol and benzol. Cloth, such as cambric or eight-ounce duck, is then passed through a vat containing the resulting mixture. The impregnated cloth is finally dried, wrapped around a mandrel and molded, under heat and pressure, to harden the bakelite.

I claim as my invention: i

11. In brushholder, the combination with a supp rting shaft and a helical biasing spring, of a brushholder finger of the type -having an enlargedIhub mo'unted for movement around said shaft and having an annular recess open at`one end for receiving said helical spring, characterized by the fact that the finger is'nearly all of a cast silicon alloy of aluminum and is provided with a finger tip of a cadmium alloy of copper having a stem embedded in said cast alloy of alumillU num, and characterized further by the fact that the said shaft is of a graphitized molded-composition product having a cloth base. 2, In a brushholder, the combination with a supporting shaft and a helical biasingl spring, of a brushholder finger of the type having an enlarged hub mounted for movement around said shaft and having an annular recess open at one end for receiving said helical spring, characterized by the fact that the finger isncarly all of a cast alloy of aluminum and is providedwith a finger tip of a cadmium alloy of copper having a stem embedded in said cast alloy of aluminum.

3. In a brushholder, the combination with a supporting shaft and a helical biasing spring, of a brushholder finger of the type having an enlarged hub mounted for movement around said shaft and having an annular recess open at one end for receiving said helical spring, characterized by the fact that the finger is provided'with a finger tip of a cadmium alloy of copper.

4. The combination with a carbon brush for a dynamo-electric machine, of a brushholder for supporting the same and a brushholder finger having a finger tip of a cadmium alloy of .copper pressing against the top of said/ brush.

5. The invention, as specified in claim 4, characterized by the fact that the finger tip has a stem embedded in a brushholder finger material having a lower melting point than said tip material, the brushholder-finger material being substantially rigid at the operating temperatures.

6. The invention, as specified in claim 4,

' characterized by the fact thatthe finger comprises a cast silicon alloy of aluminum and that said finger tip has a stem embedded in said cast alloy of aluminum.

7. The invention, as specified in claim 4, characterized by the fact that the finger comprises a cast alloy of aluminum and that said finger tip has a vstem embedded in said cast alloy of aluminum.

8. The combination with a carbon brush for a dynamo-electric machine, of-a brushholder for supporting the same and a brushholder finger having a finger tip pressing against the top vof said brush, characterized by the fact that the finger tip has a stem embedded in a brushholder finger material composed of a light metal alloy.

9. In a brushholder, the combination with a supporting shaft and a helical biasing spring, of a brushholder finger of the type having an enlarged hub mounted for movement around saidshaft and having an annular recess open at one end for receiving said helical spring, characterized by the fact that the finger. comprises a cast silicon alloy'of aluminum.

10. In a brushholder, the combination with a supporting shaft and a helical biasing spring, of a brushholder finger of the type the finger comprises a cast alloy of aluminum having an enlarged hub mounted for movement around said shaft and having an annular recess -open at one end for receiving said helical spring, characterized by the fact that and a copper finger-tip partially embedded therein.

11. The combination with) a current-collecting brush for a dynamo-electric machine,

of a brushholder for supporting the same, a brushholder-finger shaft carried by said brushholder, and a brushholder finger cary ried by said-shaft and pressing against the top of said brush, characterized by the fact that said finger comprises a cast silicon alloy of aluminum.

12. The combination with a current-collecting brush for a dynamo-electric machine, l of a brushholder for supporting the same,

a brushholder-finger shaft carried by said brushholder, and a brushholder finger carried bysaid shaft and pressing against the top of said brush, characterized by the fact that said finger comprises a cast silicon alloy of aluminum having approximately 12% of silicon.

13.*The combination with a current-collecting brush for a dynamo-electric machine,

brushholder, a brushhholder finger carried by t said shaft and pressing against the top of said brush, characterized by the fact that said finger comprises a cast silicon alloy of aluminum, and characterized further by the fact that the said shaft is of a graphitized molded-composition product.

15. The combination with a current-collecting brush for a dynamo-electric machine, of 'a brushholder for supporting the same,

a1 brushholder-finger shaft carried by said brushholder, and a brushholder finger carried by said shaft and pressing against the top of said brush, characterized by the fact that said finger comprises a cast silicon alloy of aluminum, and characterized further 1 by the fact that the said shaft is of a graphitized fibrous material. 4

16. The combination with a current-collecting brush for a dynamo-electric machine,-

of a brushholder for supporting the same,

a brushholder-finger shaft carried b said brushholder, and an aluminum-alloy rushholder finger carried by said shaft and pressing against the top of said brush, characterized/by the fact that the said shaft is of a graphitized molded-composition product having a cloth base.

-17 The combination with a current-collecting brush for a dynamo-electric machine, of a brushholder for supporting the same, a brushholder-finger shaft carried by said brushholder, and an aluminum-alloy brushholder finger carried by said shaft and pressing against the top of said brush, characterized by the fact that the said shaft is of a graphitized molded-,composiio'n product.,

18. The combination with a current-e01- lecting brush for a dynamo-eleetric machine, of a, brurshholder for supporting the same., a brushholder-inger shaft carriedA by said brushholder, :indl an -alum'inuni-:Llloy brushholder finger 'carried by \said shaft and pressing against the top of said brush, characterized by the fact that the said shaft is 10 of a graphit-,ized fibrous material. u

In testimony whereof, I have hereunto subscribed myname this 30th day of September, 1929.

1 HARRY F. HARTMAN. 

